Study on an evaluation index for noise susceptibility. I. Estimation of critical bandwidth in acoustic reflex.

A new method for estimating critical bandwidth in AR has been developed. The reflex activating sounds (RAS) consisted of a 1000 Hz pure tone, and thirteen kinds of noise centered on 1000 Hz with bandwidths of 100, 250 and 1/3-octave frequencies in 500 to 1000 Hz. A two-phase linear regression model was fitted to the sets of data which showed the relationships between the magnitude of acoustic reflex (AR) and bandwidth of RAS. The existence of a critical bandwidth was confirmed in 81 subjects with normal hearing acuity. The effects of bandwidth on magnitude of AR was not observed in two subjects, so critical bandwidth (CBW) was estimated at greater than or equal to 4000 Hz in their cases. The median value of CBW in AR was 1138 Hz in 83 subjects. Our new method, designed for practical use, may be a useful tool for estimating the critical bandwidth in AR.